// __BEGIN_LICENSE__
//  Copyright (c) 2006-2013, United States Government as represented by the
//  Administrator of the National Aeronautics and Space Administration. All
//  rights reserved.
//
//  The NASA Vision Workbench is licensed under the Apache License,
//  Version 2.0 (the "License"); you may not use this file except in
//  compliance with the License. You may obtain a copy of the License at
//  http://www.apache.org/licenses/LICENSE-2.0
//
//  Unless required by applicable law or agreed to in writing, software
//  distributed under the License is distributed on an "AS IS" BASIS,
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//  See the License for the specific language governing permissions and
//  limitations under the License.
// __END_LICENSE__


uniform sampler2DRect image;

void main() {
   vec2 coord = gl_TexCoord[0].st;

   vec4 cPixel = texture2DRect(image, coord);
   float cMin = cPixel.r;

   cPixel = texture2DRect(image, coord + vec2(1.0, 0.0));
   cMin = min(cMin, cPixel.r);

   cPixel = texture2DRect(image, coord + vec2(0.0, 1.0));
   cMin = min(cMin, cPixel.r);

   cPixel = texture2DRect(image, coord + vec2(1.0, 1.0));
   cMin = min(cMin, cPixel.r);

   gl_FragColor.r = cMin;
}
